Daniel Kammen, a professor at the University of California Berkeley’s Department of Nuclear Engineering, has stepped down from his post as a Science Envoy at the U.S. State Department — and his resignation letter had hidden message calling for President Donald Trump’s impeachment.

Kammen, who was appointed as a State Department Science Envoy under the Obama administration last year, said on Wednesday that he was resigning because of Trump’s recent comments on Charlottesville, which he said “enables racism, sexism, and harms our country and planet.”

He also posted his entire resignation letter on Twitter — and eagle-eyed observers noted that, if you take the first letter from each paragraph in the letter, they combine to spell out “IMPEACH,” as shown below.